A Vibrant Seattle Through Transportation Excellence.

Thoughtful Thursday: Why is the sidewalk bumpy?

In your travels around the city, you may have noticed these at the bottom of curb ramps and other locations.

What are these bright yellow bumps? What purpose do they serve?

This textured surface, known as a detectable warning surface, consists of bumpy domes that physically alert blind or visually impaired pedestrians that they are about to enter the street. Detectable warning surfaces are well-recognized underfoot and with a cane, and also act as a secondary confirmation for pedestrians of their whereabouts when coupled with the sound of surging traffic, grade changes on sidewalks, and other methods to assist with wayfinding.

Detectable warning surfaces also visually contrast from adjacent surfaces to provide another layer of detectability for pedestrians with low vision. While the federal standards do not specify a color that must be used, the most widely used color in Washington is yellow, as it provides a high level of visibility.

Detectable Warning Surface at Transit Platform

In addition to curb ramps, street intersections, and medians, detectable warnings also pop up in some other specific locations, such as rail and transit platforms and at rail crossings, like in Pioneer Square Tunnel Station.